The ability of hearing impaired children to function in complex multi-source environments will be studied. Children with cochlear implants (CIs) and hearing aids (HAs) spend hours every day in noisy environments such as classrooms, but their ability to hear in these environments is poorly understood. In addition, the extent to which bilateral CIs or a CI and a HA might provide a benefit compared with monaural hearing is not known. Recent thrusts by manufacturers, surgeons and parents have created a growing interest in bilateral implantation. However, this thrust must be validated with objective measures, and the tools for performing the measures must be available. This work will focus on children ages 4-10 from three groups: (1) Unilaterally implanted with a single CI, (2) Bilaterally implanted with two CIs, (3) Multi-modal with a CI in one ear and a HA in the second ear. A measurement system that can be applied in clinical setting to assess directional hearing in children rapidly and reliably, recently developed in the Pl's lab, will be employed. Computer games with puzzles and animations are implemented in order to engage the children and maintain their attention and motivation. Four specific aims are proposed with each population of children. Aim 1 will provide information regarding the potential benefits of a HA or a second CI for children's ability to detect whether a sound source is to the right or left. Aim 2 will measure the children's ability to identify source locations. Aim 3 will measure the extent to which reflections interfere with performance, which can assess the functionality of the binaural auditory pathway. Aim 4 will measure speech reception threshold (SRT) in the presence of competing sounds. This research has the potential to improve the diagnosis, selection and fitting procedures for children with hearing loss. In addition, the research might provide some insight into situations in which bilateral hearing, with dual CIs, or with a CI/HA combination, should or should not be pursued. [unreadable] [unreadable]